Cowboys in Rockville, the first thing you notice is the glasses: Everyone is holding a Mason jar full of beer.

And the second thing you notice is cowboy hats: red felt, black felt, tan, straw, some trailing a furry tail from the brim, others with peacock-feather hat bands.

Fringed jackets are the ultimate accompaniment, but western shirts and blouses are acceptable, as are lacy ruffled blouses with denim prairie skirts.

An evening at Cowboys is like going to a costume party. And if you like country-western music, Cowboys -- a friendly, reasonably priced bar and restaurant -- is a place to mingle with laid-back people who are into country, too. The only drawback is that when it's crowded, you can cut the smoke with a Bowie knife.

Last Saturday night, a band called Brahma played "Rednecking, Lovemaking Night," while couples on the dance floor dipped and spun like Tilt-a-Whirl cars at an amusement park. The dance was the Cotton-Eye Joe, not to be confused with Slappin' Leather, the Shuffle or the Texas Freeze. It was jitterbug in slow motion.

Brahma's repertoire took in southern rock -- Grateful Dead and Alabama -- as well as tried- and-true Willie Nelson, Waylon Jennings and Conway Twitty tunes.

Reaching for a nacho, a woman named Laurie from Ellicott City allowed as how she felt uncomfortable -- she usually goes out with her boyfriend -- but her friend Becky from Laurel was happily reminiscing about country musicians she'd seen in person. The two planned an evening of country-western bar- hopping.

In the back of the room, Dale Rulapaugh was helping Kim Kivett sell cowboy hats and trinkets. Hat business was slow, as it usually is on Saturday nights when the crowd is more college age. But customers were buying belt buckles, hatpins -- "Skol," "Jack Daniels" or "Lone Star Beer" pins are the most popular -- and buttons: "Cowgirls stay in the saddle longer" and "If you ain't country you ain't s..." are favored slogans.

Sitting on the lid of a trunk filled with cowboy hats, Rulapaugh surveyed the crowd. "You really have to look at the people," he said. "Then you'll be able to tell between a redneck -- I'm not a redneck -- or a college student or just a couple out having fun."

It's a fine, skinny line.

"Rednecks will have their jeans and cowboy hat and boots. . ."

That's exactly what Rulapaugh is wearing. He looks down at his jeans.

"They don't have Jordache on, okay?

"They'll have Levi's, sometimes a little bandana sticking out of their back pocket.

"There's one there -- he's from Dallas. Last week we had some rodeo riders in here. They were buying hatpins. Rednecks, cowboys, whatever you want to call them, they're spending a lot more money on this here sort of thing," he said.

Up until September, Cowboys was the Outside Inn, a rock club. But the owners, brothers Mike and Charles Patterson, like to change the format periodically; they prefer country-western music, anyway.

"Other people like rock music, new wave," said Rulapaugh. "But here, they're here for down-home." COWBOYS -- At 4828 Boiling Brook Parkway, Rockville, in the Randolph Hills shopping center. Free country dance lessons, Friday and Sunday nights from 7 to 9. 770-7530.